1. Field of the Invention
The present invention relates to spring collet chucks used on a lathe machine. In particular, the invention relates to a nosepiece assembly for a lathe which comprises a mechanically operated system for closing and opening the spring collet, wherein the closing and opening system is coupled directly through a mechanical linkage to the draw bar of the lathe.
2. State of the Art
Collet chucks, also referred to in the art as spring collets, have been used on machine tools such as lathes for a long time. The collet chuck comprises a cylindrical member that has a central, longitudinal bore. The cylindrical member has a conically flared end that is cut longitudinally into at least three sections. A work piece is positioned within the bore of the collet chuck, and the cut longitudinal pieces at the conically flared end of the cylindrical member are closed against the work piece.
Typically, the collet closer includes a sleeve through which the cylindrical collet is received. The sleeve has generally been immovably coupled to the spindle of the machine tool, and the collet is drawn into the sleeve by a draw bar on the machine tool. As the conical, flared end of the collet engages the sleeve, the cut longitudinal pieces of the collet are forced radially into firm, secure engagement with work piece. Releasing the work piece from the collet is achieved by reversing the movement of the draw bar and collet.
The collet closers as described in the preceding paragraph require longitudinal or axial movement of the collet relative to the machine tool or lathe and the work piece which can result in undesirable altering of the axial position of the work piece relative to the machine tool or lathe. An improved collet closer is disclosed in U.S. Pat. No. 4,690,415 wherein the collet is immovably mounted to the machine tool or lathe, and a floating sleeve moves back and forth on the collet. In this improved closer, the collet does not move relative to the machine tool or the work piece during closing and opening of the collet.
In accordance with U.S. Pat. No. 4,690,415, the floating sleeve is activated by a complex, self contained hydraulic system in which hydraulic fluid acts directly on the floating sleeve. Heretofore, there has been no suggestion of mechanically linking a floating sleeve such as that disclosed in U.S. Pat. No. 4,690,415 directly to the draw bar of the machine tool so as to eliminate the costly, complex, hydraulic system that is required for the operation of the floating sleeve of U.S. Pat. No. 4,690,415.